Heat exchanger

ABSTRACT

An object is to provide a heat exchanger including a resonance-prevention baffle plate disposed between a plurality of heat transfer tubes, the resonance-prevention baffle plate being obtainable and mountable readily and at lower cost. A heat exchanger  10  disposed in a flow passage of combustion gas of a boiler or the like includes: a plurality of heat transfer tubes  14  disposed in parallel and spaced from one another, an axial direction of each heat transfer tube intersecting with the combustion gas g, inside a duct wall  12  forming the flow passage of the combustion gas g; and a resonance-prevention baffle  16  having a plate shape and disposed along the combustion gas g and between the heat transfer tubes  14 , the resonance-prevention baffle including a metal foil sheet  18.

TECHNICAL FIELD

The present invention relates to a heat exchanger disposed on a boiler, for instance, the heat exchanger including a resonance-prevention baffle disposed between a group of heat transfer tubes.

BACKGROUND ART

A boiler or the like has a heat exchanger disposed in a duct housing forming a flow passage of combustion gas, the heat exchanger including a super-heater, a re-heater, and an economizer, for example. Such a heat exchanger includes a plurality of heat transfer tubes disposed inside a duct housing, and a medium such as water flowing through the heat transfer tubes is heated by combustion gas to transform into steam. The steam is sent to a steam turbine to be used for power generation. The plurality of heat transfer tubes is disposed so that the axial direction of each heat transfer tube intersects with the flow passage of combustion gas, and spaced in parallel from one another.

The heat transfer tubes are disposed in a direction orthogonal to combustion gas g inside a duct wall forming the flow passage of combustion gas. FIG. 4 is a diagram of an example of a duct wall 100 forming a flow passage of combustion gas g and heat transfer tubes 102 disposed in a grid pattern in the flow passage of the combustion gas g inside the duct wall 100. FIG. 5 is a diagram of an example of heat transfer tubes 102 disposed in a staggered pattern.

As depicted in FIG. 6, in response to combustion gas g flowing through a group of such heat transfer tubes, Karman vortices e are generated periodically downstream of a heat transfer tube 102. A generation frequency fk (Hz) of Karman vortices e can be expressed by the following expression:

Fk=St·V/D   (1)

, where St is a Strouhal number, V is a minimum gap flow rate (flow rate between heat transfer tubes), and D is an outer diameter of a heat transfer tube.

Meanwhile, a duct wall orthogonal to a flow of combustion gas and orthogonal to the axial direction of heat transfer tubes has a unique vibrational mode determined by a physical property of the combustion gas g. The unique vibrational frequency fn (Hz) is expressed by the following expression:

Fn=n·c/2L   (2)

, where n is 1, 2, 3, . . . , and c is sonic speed (depending on the temperature of the combustion gas g), and L is a distance between duct walls 100.

FIG. 7 shows a vibrational mode in the primary mode of n=1, where v represents a velocity component and p represents a pressure component. If the generation frequency fk matches one of unique vibration frequencies fn (n=1, 2, 3, . . . ), a resonance state is created, and excessive noise called tube singing is generated.

Tube singing is normally addressed and prevented by avoiding resonance by providing a resonance-prevention baffle of a plate shape along a flow of combustion gas between a group of heat transfer tubes to increase the unique vibrational frequency fn.

FIG. 8 is a diagram of an example with such a resonance-prevention baffle plate 104. In FIG. 8, a flow passage of combustion gas g is formed by a duct wall 100. Heat transfer tubes 102 are disposed in a direction orthogonal to a direction of flow of combustion gas g in the flow passage of the combustion gas g. The resonance-prevention baffle plate 104 is disposed between the heat transfer tubes 102 and along a direction of flow of the combustion gas g.

Patent Documents 1 and 2 disclose a heat exchanger including: a plurality of heat transfer tubes disposed in parallel in a flow passage of heat-exchange target gas; and a resonance-prevention baffle plate disposed along a direction of flow of a heat-exchange target fluid between the heat transfer tubes.

CITATION LIST Patent Literature

-   Patent Document 1: JPS59-012293A -   Patent Document 2: JPH05-141891A

SUMMARY Problems to be Solved

A typical resonance-prevention baffle plate has a heavy weight, and a significant amount of work hours and cost may be required to fix a resonance-prevention baffle plate with a heavy weight in a flow passage of a heat-exchange target fluid.

In view of the above problem of conventional techniques, an object of the present invention is to make configuration and installation work of a resonance-prevention baffle plate simple and less expensive.

Solution to the Problems

To achieve the above object, a heat exchanger according to an embodiment of the present invention comprises: a plurality of heat transfer tubes disposed in parallel and spaced from one another, an axial direction of each heat transfer tube intersecting with a flow passage of a heat-exchange target fluid; and a resonance-prevention baffle having a plate shape and disposed along a flow direction of the heat-exchange target fluid and between the plurality of heat transfer tubes, the resonance-prevention baffle comprising a metal foil sheet.

A resonance-prevention baffle plate has a function to increase a unique vibrational frequency fn generated inside a duct wall forming the flow passage of the heat-exchange target fluid and to differentiate the unique vibrational frequency fn from a frequency fk generated by Karman vortices e produced downstream of the heat transfer tubes.

The unique vibrational frequency fn can be increased by partitioning the flow passage of the heat-exchange target fluid and forming a boundary where the particle velocity of the heat-exchange target fluid is zero. Thus, the above function can be achieved even by a thin partition wall such as a metal foil sheet.

According to an embodiment of the present invention, the resonance-prevention baffle includes a metal foil sheet and thus can be reduced in weight. Thus, it is possible to reduce material cost and to make works required to mount and replace the resonance-prevention baffle plate simple and less expensive.

An embodiment of the present invention further comprises a rigid frame member fixed to an outer peripheral portion of the metal foil sheet. A metal foil sheet may deform in response to a heat-exchange target fluid. Thus, with the rigid frame member being fixed to the metal foil sheet, it is possible to apply rigidity to the metal foil sheet. Accordingly, it is possible to prevent deformation of the metal foil sheet and to maintain rigidity such that the metal foil sheet does not deform in response to a flow of a heat-exchange target fluid, without increasing too much weight.

In an embodiment of the present invention, the resonance-prevention baffle is fixed to at least a part of the plurality of heat transfer tubes by a fixing member.

As described above, since the resonance-prevention baffle of the present invention can be reduced in weight, it is possible to mount the resonance-prevention baffle to the heat transfer tube readily by using a fixing member with less strength. Furthermore, since the resonance-prevention baffle has less weight, it is sufficient if the resonance-prevention baffle is fixed to only a part of the heat exchanger tubes, which reduces the load of mounting work.

In an embodiment of the present invention, the fixing member comprises a U-shape bolt disposed so as to surround the heat transfer tube and screwed to the resonance-prevention baffle at opposite ends. With the U-shape bolt having the above configuration, it is possible to further facilitate mounting work.

In an embodiment of the present invention, the plurality of heat transfer tubes is disposed linearly along the flow direction of the heat-exchange target fluid, and the resonance-prevention baffle is formed into a flat plate shape and disposed along the flow direction of the heat-exchange target fluid.

Thus, it possible to readily insert the resonance-prevention baffle plate between the heat transfer tubes, which are ready-made members, and to set the resonance-prevention baffle plate in a predetermined position. Thus, it is possible to mount or replace the resonance-prevention baffle without removing the heat transfer tubes, which are ready-made members. Further, it is no longer necessary to install the heat transfer tubes after mounting the resonance-prevention baffle, which makes it possible to reduce a considerable amount of man hours for mounting and replacing.

Advantageous Effects

According to an embodiment of the present invention, the resonance-prevention baffle includes a metal foil sheet and thus has less weight, which makes it possible to make mounting work of the resonance-prevention baffle simple and less expensive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front cross-sectional view of a heat exchanger according to the first embodiment of the present invention.

FIG. 2 is a pre-assembly perspective view of a resonance-prevention baffle plate of the heat exchanger.

FIG. 3 is a post-assembly perspective view of the resonance-prevention baffle plate.

FIG. 4 is a front cross-sectional view of a general grid-pattern arrangement of heat transfer tubes.

FIG. 5 is a front cross-sectional view of a general staggered arrangement of heat transfer tubes.

FIG. 6 is a diagram for describing Karman vortices e generated downstream of a heat transfer tube.

FIG. 7 is a diagram for describing unique vibration generated inside a duct wall of a heat exchanger.

FIG. 8 is a front cross-sectional view of a typical heat exchanger.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise particularly specified, the sizes, materials, shapes, and relative arrangement or the like of constituent components described in these embodiments are not intended to limit the scope of this invention.

A heat exchanger according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 3. The present embodiment is an example in which a heat exchanger 10 according to the first embodiment of the present invention is applied to a heat exchanger such as a super-heater, a re-heater, and an economizer, or to a waste-heat recovery boiler, for instance, disposed on a steam boiler incorporated into a thermal power generation plant.

In FIG. 1, a flow passage of combustion gas g is formed by a duct housing constituting the heat exchanger 10 of the present embodiment. A plurality of heat transfer tubes 14 is disposed inside a duct wall 12 constituting the duct housing. The duct housing has, for instance, a quadrilateral or circular cross section.

The heat transfer tubes 14 are disposed in parallel and spaced from one another, and the axial direction of each heat transfer tube 14 is orthogonal to the combustion gas g. The heat transfer tubes 14 are arranged in a grid pattern. Specifically, the heat transfer tubes 14 are arranged in lines extending linearly in a direction of flow of the combustion gas g, and also in a direction orthogonal to the direction of flow of the combustion gas g.

The combustion gas g exchanges heat with a medium such as water flowing inside each heat transfer tube 14 while flowing between the heat transfer tubes 14, and the medium such as water is heated by the combustion gas g to transform into steam. The steam is sent to a steam turbine to be used for power generation.

Two resonance-prevention baffles 16 are inserted between the heat transfer tubes 14 and fixed to the heat transfer tubes 14. The resonance-prevention baffle 16 includes a metal foil sheet 18 having a flat surface and is disposed along the direction of flow of the combustion gas g. As described above, the resonance-prevention baffle 16 is disposed to partition the flow passage of the combustion gas g, thereby forming a boundary in a flow rate of the combustion gas g. Accordingly, it is possible to increase a resonance frequency generated inside the duct wall 12.

As described above, the unique vibrational frequency fn of the unique vibrational mode formed inside the duct wall 12 by the flow of the combustion gas g is differentiated from the generation frequency fk of Karman vortices e generated behind each heat transfer tube 14, which makes it possible to prevent generation of excessive noise.

As illustrated in FIGS. 2 and 3, the resonance-prevention baffle plate 16 includes a metal foil sheet 18 of a quadrilateral shape made of high-temperature stainless steel (SUH 409L) having a thickness of 10 to 1000 μm, for example, 20 μm. It should be noted that the material of the metal foil sheet 18 is selected on the basis of the temperature of a heat-exchange target fluid, and the thickness of the metal foil sheet 18 is selected on the basis of the hardness, viscosity, or the like of the selected material.

Further, the length of a side of the metal foil sheet used in the present invention is determined on the basis of the length of a boiler casing and the number of stages of a heat exchanger, and is 20 m (duct width)×2 m (number of stages of a heat exchanger), for instance.

The metal foil sheet 18 deforms in response to a flow of combustion gas. Thus, an outer peripheral portion of the metal foil sheet 18 is nipped by frame members 20, 20 having rigidity from both sides. The two frame members 20 are fastened by bolts 22 and nuts 24 at where needed. It should be noted that head portions of the bolts 22 and the nuts 24 should be buried into the frame members 20, 20 as much as possible so as not to generate a turbulence in the flow of combustion gas.

As illustrated in FIG. 1, the resonance-prevention baffle plate 16 is fixed to the heat transfer tubes 14 by using a U-shape bolt 26. Specifically, the U-shape bolt 26 has male screws formed on opposite ends, and is disposed so as to surround the heat transfer tube 14, and the male screws of the opposite ends of the U-shape bolt 26 are engaged with female screw holes formed on the resonance-prevention baffle plate 16. Alternatively, the opposite ends may be inserted through holes formed on the resonance-prevention baffle plate 16, and the male screws may be engaged with nuts 28 to fix the resonance-prevention baffle plate 16 to the heat transfer tube 14.

It should be noted that a position of mounting using the U-shape bolt 26 may be a position required to achieve a necessary fixing strength of the resonance-prevention baffle 16.

According to the present embodiment, the resonance-prevention baffle plate 16 includes the metal foil sheet 18 and thus can be reduced in weight. Thus, it is possible to reduce material cost and to make works required to mount and replace the resonance-prevention baffle plate 16 simple and less expensive.

Further, with the outer peripheral portion of the metal foil sheet 18 fastened from both sides by the two frame members 20, 20 with rigidity, it is possible to maintain rigidity so as not to deform in response to a flow of combustion gas without increasing too much weight.

Further, since the resonance-prevention baffle plate 16 can be reduced in weight, it is possible to mount the resonance-prevention baffle plate 16 to the heat transfer tube 14 readily by using a fixing member with less strength. Thus, it is possible to fix the resonance-prevention baffle plate 16 firmly by using a less expensive fixing member.

Furthermore, since the resonance-prevention baffle plate 16 has less weight, it is sufficient if the resonance-prevention baffle plate 16 is fixed to only a part of the heat transfer tubes 14, which reduces the load of mounting work.

Still further, since the U-shape bolt 26 is used as a fixing unit of the resonance-prevention baffle plate 16, it is possible to simplify the mounting work even further.

Further, the heat transfer tubes 14 are disposed in a grid pattern and the resonance-prevention baffle plate 16 is formed into a flat plate shape, which makes it possible to readily insert the resonance-prevention baffle plate 16 between the heat transfer tubes 14, which are ready-made members, and to set the resonance-prevention baffle plate 16 in a predetermined position.

Thus, it is possible to mount or replace the resonance-prevention baffle plate 16 without removing the heat transfer tubes 14, which are ready-made members, or without mounting the heat transfer tubes 14 after mounting the resonance-prevention baffle plate 16.

In the above described embodiment, the present invention is applied to a heat exchanger including heat transfer tubes disposed in a grid pattern. However, the present invention can be also applied to a heat exchanger including heat transfer tubes disposed in a staggered or zig-zag pattern by modifying a method to fix a metal foil sheet.

INDUSTRIAL APPLICABILITY

According to the present invention, for a heat exchanger including a plurality of heat transfer tubes disposed in parallel and a resonance-prevention baffle plate disposed between the heat transfer tubes, it is possible to make configuration and installation work of a resonance-prevention baffle plate simple and less expensive.

DESCRIPTION OF REFERENCE NUMERALS

-   10 Heat exchanger -   12, 100 Duct wall -   14, 102 Heat transfer tube -   16, 104 Resonance-prevention baffle plate -   18 Metal foil sheet -   20 Frame member -   22 Bolt -   24, 28 Nut -   26 U-shape bolt -   e Karman vortex -   g Combustion gas 

1. A heat exchanger, comprising: a plurality of heat transfer tubes disposed in parallel and spaced from one another, an axial direction of each heat transfer tube intersecting with a flow passage of a heat-exchange target fluid; a resonance-prevention baffle having a plate shape and disposed along a flow direction of the heat-exchange target fluid and between the plurality of heat transfer tubes, the resonance-prevention baffle comprising a metal foil sheet; and a rigid frame member fixed to an outer peripheral portion of the metal foil sheet.
 2. (canceled)
 3. The heat exchanger according to claim 1, wherein the resonance-prevention baffle is fixed to at least a part of the plurality of heat transfer tubes by a fixing member.
 4. The heat exchanger according to claim 3, wherein the fixing member comprises a U-shape bolt disposed so as to surround the heat transfer tube and screwed to the resonance-prevention baffle at opposite ends.
 5. The heat exchanger according to claim 1, wherein the plurality of heat transfer tubes is disposed linearly along the flow direction of the heat-exchange target fluid, and wherein the resonance-prevention baffle is formed into a flat plate shape and disposed along the flow direction of the heat-exchange target fluid. 